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Journal of Lipid Research, Vol. 7, 27-37, January 1966
Copyright © 1966 by Lipid Research, Inc.

Origin of milk cholesterol in the rat: dietary versus endogenous sources

R. Clarenburg and I. L. Chaikoff

Department of Physiology, University of California, Berkeley, California

Slices of mammary gland from lactating rats, incubated with acetate-1-¹⁴C or mevalonate-2-¹⁴C, synthesized cholesterol-¹⁴C.

Within 2 min of an intravenous injection of 1 ml of a suspension of chylomicrons containing cholesterol-4-¹⁴C, mammary glands of lactating rats removed as much as 29% of the labeled cholesterol; those of 2-day-postlactating rats removed none.

Rats were fed a diet containing 0.05% cholesterol-4-¹⁴C from 7 days prepartum to 20 days postpartum. At isotopic equilibrium, the relative specific activities of milk and dietary cholesterol indicated a dietary origin for 11% of the milk cholesterol. The extent to which endogenous sources—liver and mammary gland—contributed cholesterol to milk proved entirely dependent on whether dietary cholesterol, in the form of chyle lipo-proteins, was first processed by liver or taken up directly by mammary gland. Lack of information regarding the extent to which chyle cholesterol is removed from blood under physiological conditions by mammary gland and other tissues precludes precise assessment of the endogenous contributions to milk cholesterol and, moreover, casts doubt on the quantitative interpretability of cholesterol-¹⁴C-feeding experiments reported in the literature.

Supplementary key words lactation • rat • mammary gland • cholesterol • biosynthesis • uptake • chylomicron • dietary • cholesterol-4-¹⁴C • liver • isotopic equilibrium • difficulties • interpretation

Submitted on May 27, 1965
Accepted on August 23, 1965

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